Processing of partial frames and partial superframes

ABSTRACT

A system receives a set of datagrams and forms frames based on the datagrams, where at least one of the frames includes data associated with multiple ones of the datagrams. The system writes the frames to memory to form superframes in the memory, where each of the superframes includes multiple ones of frames. The system reads the superframes from the memory, recreates the datagrams based on the superframes, and outputs the datagrams.

BACKGROUND

1. Field of the Invention

Implementations consistent with the principles of the invention relategenerally to data communication and, more particularly, to the use of ascalable central memory switching fabric architecture within a datatransfer device.

2. Description of Related Art

A typical shared memory switching architecture includes input and outputports connected via a shared memory switching fabric. Typically, ashared memory switching architecture is used only when the desiredaggregate system bandwidth can be achieved using a memory data widthequal to or less than a cell size (for cell systems) or a minimum packetsize (for packet systems). The shared memory switch architecturesometimes includes multiple memory subsystems. In this case, statisticalor hash-based load balancing may be used between the memory subsystems.These approaches can be blocking and/or slower than wire speed.

For high bandwidth systems, lightly buffered or unbuffered cross-pointarchitectures are typically used. These architectures often includedelay-bandwidth buffer memory at the ingress and egress line cards. As aresult, the memory bandwidth of the system is reduced to that of theline card instead of that of the entire system. With the cross-pointarchitecture, each packet is written and read twice at each of the linecards. Therefore, the total system memory bandwidth required is doublethat of a shared memory switching architecture. Further, cross-pointarchitectures typically have significant blocking characteristics on aport-to-port basis when there are many sub-ports (streams) per linecard.

SUMMARY

According to one aspect, a data transfer device may include a set ofingress units, a set of egress units, and a memory connected to theingress units and the egress units. At least some of the ingress unitsmay be configured to receive a group of datagrams, form a frame from oneor more of the datagrams, and output the frame to the memory. The memorymay be configured to receive the frames from the ingress units, storethe frames to form superframes, and output the superframes to the egressunits. At least some of the egress units may be configured to receiveone of the superframes from the memory, reassemble a datagram from datain the superframe and/or a subsequent superframe, and output thedatagram.

According to another aspect, a method may include receiving a group ofdatagrams; forming frames based on the datagrams, where each of theframes may include data associated with one or more of the datagrams;writing the frames to memory to form superframes in the memory, whereeach of the superframes may include multiple frames; reading thesuperframes from the memory; reassembling the datagrams based on thesuperframes; and outputting the reassembled datagrams.

According to yet another aspect, an ingress line card is associated witha data transfer device. The ingress line card may include an interfaceto receive a group of datagrams and form frames based on the datagrams.Each of the frames may include a header portion and a data portion,where the data portion is capable of storing data associated withmultiple datagrams, and the header portion may identify a break betweendatagrams when the data portion stores data associated with multipledatagrams. The ingress line card may also include a memory to store thedatagrams prior to the frames being formed based on the datagrams.

According to a further aspect, an egress line card is associated with adata transfer device. The egress line card may include an interface toreceive a group of superframes, where each of the superframes mayinclude data associated with multiple datagrams, and at least one of thesuperframes may include data less than an entire datagram. The interfacemay also determine whether all data associated with a datagram isincluded in one or more of the superframes and reassemble the datagramwhen all data associated with the data is included in one or more of thesuperframes. The egress line card may also include a memory to storedata associated with the datagrams prior to the datagrams beingreassembled.

According to another aspect, a data transfer device may include aningress unit, a central switching fabric, and an egress unit. Theingress unit may receive a group of datagrams, where each of thedatagrams may be associated with an egress point. The ingress unit mayalso pack data associated with the datagrams into first containers,where each of the first containers may be capable of storing dataassociated with multiple datagrams. The central switching fabric maypack a group of the first containers into each of a group of secondcontainers, where the first containers associated with a particular oneof the second containers may include data associated with datagramsassociated with a same egress point. The egress unit may receive one ormore of the second containers from the central switching fabric,recreate the datagrams from data in the one or more of the secondcontainers, and output the datagrams.

According to a further aspect, a data transfer device may include acentral switching fabric. The central switching fabric may include acentral shared memory to receive first data of a first length, store thefirst data as second data of a second length, where the second length islarger than the first length, and output the second data.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate an embodiment of the inventionand, together with the description, explain the invention. In thedrawings,

FIG. 1 is an exemplary diagram of a device in which systems and methodsconsistent with the principles of the invention may be implemented;

FIG. 2 is an exemplary block diagram of a portion of an ingress linecard of FIG. 1 according to an implementation consistent with theprinciples of the invention;

FIG. 3 an exemplary diagram of a frame according to an implementationconsistent with the principles of the invention;

FIG. 4 is an exemplary diagram of a portion of the egress line card ofFIG. 1 according to an implementation consistent with the principles ofthe invention;

FIG. 5 is an exemplary diagram of a portion of the central switchingfabric of FIG. 1 according to an implementation consistent with theprinciples of the invention;

FIG. 6 is an exemplary diagram of a portion of the scheduler/controllerof FIG. 5 according to an implementation consistent with the principlesof the invention;

FIG. 7 is an exemplary diagram of a portion of the memory of FIG. 5according to an implementation consistent with the principles of theinvention;

FIG. 8 is a flowchart of an exemplary operation for processing datagramsaccording to an implementation consistent with the principles of theinvention; and

FIGS. 9-14 illustrate processing that may be performed with regard tothe exemplary operation of FIG. 8 according to an implementationconsistent with the principles of the invention.

DETAILED DESCRIPTION

The following detailed description of the invention refers to theaccompanying drawings. The same reference numbers in different drawingsmay identify the same or similar elements. Also, the following detaileddescription does not limit the invention. Instead, the scope of theinvention is defined by the appended claims and equivalents.

Implementations consistent with the principles of the invention relateto a central shared memory switching fabric that is scalable, reducesthe amount of memory (buffering) needed, and is more ideal in terms ofblocking over existing switching fabrics. All of the memory bandwidth isavailable as needed for each incoming datagram regardless of thedestination of the incoming datagram. In other words, sufficient memorybandwidth is available even in the extreme case where datagrams from allof the inputs are destined for the same output.

Exemplary Device

FIG. 1 is an exemplary diagram of a device 100 in which systems andmethods consistent with the principles of the invention may beimplemented. In one implementation, device 100 may correspond to a datatransfer device, such as a router, a switch, a gateway, a bridge, or thelike. Device 100 may include a set of ingress line cards 110-1 through110-N (collectively referred to as “ingress line cards 110”), a set ofegress line cards 120-1 through 120-N (collectively referred to as“egress line cards 120”), and a central switching fabric 130.

While FIG. 1 shows that device 100 includes separate sets of ingressline cards 110 and egress line cards 120, the functions of an ingressline card and an egress line card may be implemented within a singleline card. In other words, a single line card may include ingress linecard functionality as well as egress line card functionality. In anotherimplementation, ingress line cards 110 and egress line cards 120 may bephysically separate line cards and may differ in number. For example,there may be more or fewer ingress line cards 110 than egress line cards120. In either implementation, ingress line cards 110 and egress linecards 120 may connect to central switching fabric via wired, wireless,and/or optical connections.

Ingress line cards 110 may include input units that receive streams ofdatagrams on ingress links and make the datagrams available to centralswitching fabric 130. A “datagram,” as used herein, may refer to anytype or form of data, including packet and non-packet data. Some ofingress line cards 10 may differ in speed and/or bandwidth. For example,a first ingress line card that connects to the core of a network, suchas the Internet, may include more speed and/or bandwidth than a secondingress line card that connects to the edge of the network. In thiscase, the first ingress line card may include more ingress links (thatmay possibly be bound together as a single stream) than the secondingress line card.

FIG. 2 is an exemplary block diagram of a portion of ingress line card110-0 according to an implementation consistent with the principles ofthe invention. Other ones of ingress line cards 10 may include the sameor similar components.

As shown in FIG. 2, ingress line card 110-0 may include an ingressfabric interface 210 and a memory 220. Ingress fabric interface 210 mayinclude a field programmable gate array (FPGA) or an applicationspecific integrated circuit (ASIC). Ingress fabric interface 210 mayreceive streams of datagrams over one or more ingress links and generateframes based on the datagrams.

A frame may be thought of as a container that includes a fixed amount ofdata associated with one or more datagrams. In one implementation, aframe is 64 bytes in length. In another implementation, a frame is 256bytes in length. In yet another implementation, a frame may have alength different from 64 or 256 bytes. A frame may be larger, smaller,or the same size as a datagram. Because the datagrams may differ insize, a frame may be larger than some datagrams, smaller than otherdatagrams, and the same size as yet other datagrams.

Ingress fabric interface 210 may pack datagrams into frames withoutregard to the beginnings and endings of the datagrams. In other words,the datagrams need not be aligned with the start and end of the frame. Aframe may be filled quickly or gradually as datagrams arrive on theingress link(s).

FIG. 3 is an exemplary diagram of a frame 300 according to animplementation consistent with the principles of the invention. Frame300 may include a header portion 310 and a data portion 320. Headerportion 310 may be generated by ingress fabric interface 210 (FIG. 2).Header portion 310 may be passed along with frame 300 within device 100and may be used to reassemble the datagrams at egress line cards 120. Inone implementation, header portion 310 is not used by central switchingfabric 130, but is simply forwarded by central switching fabric 130along with frame 300.

As shown in FIG. 3, header portion 310 may include frame source cardfield 311, frame partial field 312, frame valid field 313, frame datavalid field 314, frame data end of datagram (EOD) field 315, frame datastart of datagram (SOD) field 316, frame data prior EOD pointer (PTR)field 317, and frame queue field 318. In other implementations, headerportion 310 may contain more, fewer, or different pieces of information.

Frame source card field 311 may identify the ingress line card thatgenerated frame 300. Frame queue field 318 may identify a queue withwhich frame 300 is associated. As described below, the queue may beassociated with a particular egress point of device 100, Frame sourcecard field 311 and frame queue field 318 may be used for reassembly byan egress line card.

Frame partial field 312 may indicate whether frame 300 is complete. Insome situations, it may be beneficial for an ingress line card to outputa frame that is not completely filled with data from one or moredatagrams. When frame partial field 312 indicates that frame 300 is notcomplete, then data portion 320 may be less than filled with data fromone or more datagrams.

Frame valid field 313 may indicate whether frame 300 is valid. Framedata valid field 314 may indicate whether data portion 320 of frame 300is completely empty. Frame data EOD field 315 may identify where the endof a datagram occurs within data portion 320. Frame data SOD field 316may identify where the start of a datagram occurs within data portion320. Frame data EOD field 315 and frame SOD field 316 may be used toidentify a break between datagrams in frame 300 and identify where thisbreak occurs. Frame data prior EOD pointer field 317 may indicatewhether frame 300 contains one complete datagram.

Data portion 320 may store data associated with one or more datagrams.When data portion 320 stores data associated with multiple datagrams,the data may be packed together with no holes or gaps between them andwithout regard to the beginnings and endings of the datagrams. In otherwords, data portion 320 may store all or part of an entire datagram andmay store parts of two or more datagrams.

Returning to FIG. 2, ingress fabric interface 210 may accumulate datafor frames and when a frame is complete, it may output the frame and anotification. The notification may inform central switching fabric 130(FIG. 1) that ingress line card 110-0 is outputting a frame. Thenotification may include information that identifies the egress pointwith which the frame is associated. An egress point may correspond to anegress link or port of an egress line card or some finer granularity,such as a class of traffic, a priority of traffic, a weight assigned toparticular traffic or a particular link or port, etc.

Memory 220 may include a memory device, such as a SRAM. Memory 220 mayinclude a number of bins (e.g., queues) to store datagrams for frames.In one implementation, memory 220 may include a bin for each egresspoint. Memory 220 may accumulate datagrams for a particular egress pointin a corresponding bin until a complete frame's worth of data isaccumulated. At this point, ingress fabric interface 210 may generateand output the frame.

Returning to FIG. 1, egress line cards 120 may include egress units thatreceive superframes from central switching fabric 130, reassembledatagrams from the superframes, and make the datagrams available toegress links. A superframe may be considered a container that includes afixed number of frames, equal to or greater than two frames. In oneimplementation, a superframe includes sixteen frames. In anotherimplementation, a superframe may include more or fewer frames.

Similar to ingress line cards 110, some of egress line cards 120 maydiffer in speed and/or bandwidth. For example, a first egress line cardthat connects to the core of a network, such as the Internet, mayinclude more speed and/or bandwidth than a second egress line card thatconnects to the edge of the network. In this case, the first egress linecard may include more egress links (that may possibly be bound togetheras a single stream) than the second egress line card.

FIG. 4 is an exemplary block diagram of a portion of egress line card120-0 according to an implementation consistent with the principles ofthe invention. Other ones of egress line cards 120 may include the sameor similar components.

As shown in FIG. 4, egress line card 120-0 may include an egress fabricinterface 410 and a memory 420. Egress fabric interface 410 may includea FPGA or an ASIC. Egress fabric interface 410 may receive superframes,reassemble datagrams from the superframes, and make the datagramsavailable to egress links. Egress fabric interface 410 may useinformation in the headers of the frames within the superframes toidentify datagram portions that belong to the same datagrams. Forexample, egress fabric interface 410 may use information in frame sourcecard field 311 and frame queue field 318 (FIG. 3) to identify theparticular datagram with which a frame is associated. Based on thisinformation, egress fabric interface 410 may reassemble the datagramsand output the datagrams on one or more egress links.

Memory 420 may include a memory device, such as a SEAM. Memory 420 mayinclude a number of bins (e.g., queues) to store data associated withdatagrams. In one implementation, memory 420 may include a bin for eachegress point and ingress point combination. An ingress point maycorrespond to an ingress link or port of an ingress line card or somefiner granularity, such as a class of traffic, a priority of traffic, aweight assigned to particular traffic or a particular link or port, etc.Therefore, memory 420 may have a larger memory requirement than memory220 (FIG. 2) of ingress line cards 110. Memory 420 may accumulate dataassociated with datagrams for a particular egress point and ingresspoint combination in a corresponding bin until all of the data iscollected and the datagram can be reassembled. At this point, egressfabric interface 410 may output the datagram on an egress link.

Returning to FIG. 1, central switching fabric 130 may be implemented ona circuit card. Alternatively, there might be multiple planes of centralswitching fabrics 130 implemented on one or more circuit cards.Generally, central switching fabric 130 may store frames and scheduletheir transmission via egress line cards 120.

FIG. 5 is an exemplary diagram of a portion of central switching fabric130 according to an implementation consistent with the principles of theinvention. As shown in FIG. 5, central switching fabric 130 may includea multiplexer 510, a scheduler/controller (S/C) 520, a central sharedmemory 530, and a set of buffers 540-0 through 540-N (collectivelyreferred to as “buffers 540”).

Multiplexer 510 may receive frames from ingress line cards 110 andforward them to memory 530. In one implementation, multiplexer 510 maybe controlled to select certain frames to forward to memory 530. Forexample, S/C 520 may control multiplexer 510 to forward a frame atsubstantially the same time that S/C 520 outputs a write addresscorresponding to that frame. Alternatively, multiplexer 510 may selectframes to forward according to a schedule, such as a round robinschedule.

S/C 520 may include a FPGA or an ASIC. S/C 520 may operate as a masterbookkeeper for memory 530. S/C 520 may receive notifications fromingress line cards 110 when ingress line cards 110 send frames tomultiplexer 510. S/C 520 may generate write addresses for storing theframes in memory 530 and read addresses for reading superframes frommemory 530.

FIG. 6 is an exemplary diagram of a portion of S/C 520 according to animplementation consistent with the principles of the invention. As shownin FIG. 6, S/C 520 may include a write address generator 610, a readaddress generator 620, a memory pool manager 630, and a memory pool 640.Write address generator 610 may determine and generate write addressesfor storing frames as superframes in memory 530. Read address generator620 may determine and generate read addresses for reading superframesfrom memory 530.

Memory pool manager 630 may control the generation of write and readaddresses by write address generator 610 and read address generator 620,respectively. Memory pool manager 630 may also track the addresses atwhich superframes are stored in memory 530. Memory pool manager 630 maytrack these addresses in queues of references to memory locations withinmemory 530 that contain data that needs to be sent to egress line cards120. As described below, these queues may be maintained within memorypool 640.

Memory pool manager 630 may store frames associated with the same egresspoint together in the same superframe in memory 530. Memory pool manager630 may allocate a buffer representing the superframe to a queueassociated with the egress point and track how complete the superframeis. With the arrangement described herein, it does not matter whetherthe superframe gets completed gradually over time from a single ingressline card or all at once from multiple, possibly all, ingress linecards.

When memory pool manager 630 determines that the superframe is complete(i.e., filled with frames), memory pool manager 630 may enqueue it intoa queue or list of superframes that are complete and pendingtransmission via a particular egress point. Because the superframe isbigger, possibly many times bigger, than a frame, memory pool manager630 may have several clock cycles to identify the next superframe to beread from memory 530. Memory pool manager 630 may service each of thequeues or lists of completed superframes equally (e.g., according to around robin schedule). When priorities, weights, etc. are associatedwith the queues/lists, it may take memory pool manager 630 several clockcycles to determine which superframe is to be read next.

Memory pool 640 may include a memory device, such as a SRAM. Memory pool640 may maintain a number of queues to store references to locations inmemory 530. Memory pool 640 may also maintain a number of lists orqueues of completed superframes. At a minimum, memory pool 640 mayinclude one queue/list for each of egress line cards 120. In practice,however, memory pool 640 may include multiple queues/lists for each ofegress line cards 120. For example, a queue/list may be set up tocorrespond to an output port of an egress line card 120, a class oftraffic on the output port, a priority associated with the class oftraffic on the output port, or some finer or other degree ofgranularity.

The queues/lists may be set up as point to point (a single ingress pointto a single egress point), point to multi-point (a single ingress pointto multiple egress points), multi-point to point (multiple ingresspoints to a single egress point), or multi-point to multi-point(multiple ingress points to multiple egress points). In the point topoint case, a queue/list may be set up to store information (e.g.,references to locations in memory 530 or information regarding completedsuperframes) associated with frames from a single ingress point destinedfor a single egress point. In the point to multi-point case, aqueue/list may be set up to store information (e.g., references tolocations in memory 530 or information regarding completed superframes)associated with frames from a single ingress point destined for multipleegress points. In the multi-point to point case, a queue/list may be setup to store information (e.g., references to locations in memory 530 orinformation regarding completed superframes) associated with frames frommultiple ingress points destined for a single egress point. In themulti-point to multi-point case, a queue/list may be set up to storeinformation (e.g., references to locations in memory 530 or informationregarding completed superframes) associated with frames from multipleingress points destined for multiple egress points.

The queues/lists may be maintained as linked lists within memory pool640. This allows flexibility in the size of any particular queue/listand the location at which an item for the queue/list is stored withinmemory pool 640. For each queue/list, memory pool 640 may include a headpointer that identifies the top of the queue/list, a tail pointer thatidentifies the bottom of the queue/list, and for each item in thequeue/list, a pointer to the next item in the queue/list. Memory pool640 may also track how many items are in each queue/list.

Returning to FIG. 5, memory 530 may store frames as superframes. Memory530 may contain sufficient bandwidth to write from all ingress linecards 110. As a result, there is no congestion at multiplexer 510.

FIG. 7 is a diagram of a portion of memory 530 according to animplementation consistent with the principles of the invention. As shownin FIG. 7, memory 530 may include a set of memory cards 710-1 through710-M (collectively referred to as “memory cards 710”). Each of memorycards 710 may include a memory device, such as a SRAM or DRAM. Theactual number of memory cards 710 included in memory 530 may be based onone or more network parameters (e.g., the throughput of device 100, theamount of network traffic traversing device 100, etc.). The bandwidth ofmemory 530 can be increased by adding one or more additional memorycards 710. Memory cards 710 may function as a logical memory device witha single read address, a single write address, and a wide datainput/output.

One of memory cards 710 may be used as a backup memory. For example,this memory card may include an exclusive OR (XOR) of the data in theother memory cards. Therefore, when a memory card fails, the backupmemory card can be used to recreate the data in the failed memory cardand it can be hot swapped with the failed memory card.

Returning to FIG. 5, buffers 540 may include rate-matching memorydevices, such as first-in, first-out (FIFO) memories. The read bandwidthof memory 530 may be much larger than the bandwidth that can be acceptedby or that is desired by egress line cards 130. Buffers 540 may adjustthe rate to that handled by egress line cards 130. It may also bedesirable to include rate-matching memory devices on the ingress sidebetween ingress line cards 110 and memory 530 (not shown).

Exemplary Processing

FIG. 8 is a flowchart of an exemplary operation for processing datagramsaccording to an implementation consistent with the principles of theinvention. FIGS. 9-14 illustrate processing that may be performed withregard to the exemplary operation of FIG. 8 according to animplementation consistent with the principles of the invention.

Processing may begin with the receipt of datagrams on ingress links(block 810). As shown in FIG. 9, ingress line card ILC0 may receive astream of datagrams. Ingress line card ILC0 may store the datagrams inbins based on the egress points with which the datagrams are intended.The bins may be considered frame containers that may be equal in size tothe size of a frame.

Frames may be formed based on the datagrams (block 820). As shown inFIG. 9, ingress line card ILC0 may track the fullness of the bins. Oncea bin is filled with a framers worth of data, regardless of thebeginning and ending of any datagram within the bin, ingress line cardILC0 may form a frame based on the data in the bin. For example, ingressline card ILC0 may generate a header portion 310 (FIG. 3) and pack thedata from the bin into a data portion 320 of a frame.

The completed frames and notifications may be output to centralswitching fabric 130 (block 830). As shown in FIG. 9, ingress line cardILC0 may output frame F-0 and notification NOTIF-0. Frame F-0 maycorrespond to a frame that has been generated by ingress line card ILC0.Notification NOTIF-0 may inform central switching fabric 130 that frameF-0 has been (or is being) output by ingress line card ILC0.

Write addresses may be generated for storing the frames in memory assuperframes (block 840). In one implementation, a frame may be stored inmemory every clock cycle. As shown in FIG. 10, scheduler/controller S/Cmay receive notification NOTIF-0 from ingress line card ILC0 S/C maygenerate a write address for storing frame F-0 in memory. As shown inFIG. 11, the write address may be used to identify the location at whichframe F-0 is stored within the memory. As shown in FIG. 12, frame F-0may be stored within a superframe in memory. As explained above, asuperframe may be associated with a particular egress point. Therefore,as shown in FIG. 12, frames F-J, F-R, F-Y, and F-0 may be associatedwith the same egress point.

References to the locations in memory that the superframes are storedmay be maintained (block 850). As shown in FIG. 10, the memory poolmanager may store a reference to the location at which the superframecontaining frame F-0 is stored in memory in one of several queues. Theparticular queue in which the reference is stored may correspond to theegress point associated with the superframe.

Read addresses may be generated for reading superframes from memory(block 860). In one implementation, a superframe is read from memoryevery multiple number of a clock cycle (e.g., every 16 clock cycles). Asshown in FIG. 13, the memory pool manager within scheduler/controllerS/C may identify a queue/list that contains a completed superframe. Forexample, the memory pool manager might determine that superframe SF-D isthe next superframe to be read from memory. The read address generatormay generate a read address corresponding to the location in the memorythat stores superframe SF-D. As shown in FIG. 14, the read address maybe used to cause the memory to output superframe SF-D.

Datagrams may be reassembled from the superframes (block 870). As shownin FIG. 14, egress line card ELC0 may receive superframe SF-D and storeit in the appropriate bin. The particular bin in which superframe SF-Dis stored may correspond to the egress point associated with superframeSF-D. Egress line card ELC0 may use the data in the bin to reassemblethe datagrams. A superframe may include all or a portion of the dataassociated with a datagram. If the superframe includes all of the datafor a datagram, egress line card ELC0 may reassemble the datagram basedon this data. If the superframe includes less than all of the data for adatagram, egress line card ELC0 may buffer the data until the rest ofthe data arrives in a subsequent superframe.

The datagrams may be output on one or more egress links (block 880). Asshown in FIG. 14, once egress line card ELC0 reassembles a datagram, itmay schedule the datagram for transmission via the appropriate egresslink, or links. The datagram may then be output on the egress link, orlinks.

CONCLUSION

Systems and methods consistent with the principles of the invention mayprovide a scalable central shared memory switching fabric that mayfacilitate the transmission of datagrams in an efficient andnon-blocking manner. The central shared memory switching fabric mayprovide these benefits even when implemented by low performancecomponents, such as FPGAs and SRAMs.

The foregoing description of preferred embodiments of the inventionprovides illustration and description, but is not intended to beexhaustive or to limit the invention to the precise form disclosed.Modifications and variations are possible in light of the aboveteachings or may be acquired from practice of the invention.

For example, while a series of acts has been described with regard toFIG. 8, the order of the acts may differ in other implementationsconsistent with the principles of the invention. Also, non-dependentacts may be performed in parallel.

Also, ingress and egress line cards have been described without ingressand egress buffering. In another implementation, the ingress line cardsand/or the egress line cards may include such buffering. This bufferingmay be used by the ingress line cards to hold data when queues of thescheduler/controller exceed a threshold. In this case, thescheduler/controller may send out information on the lengths of itsqueues to the ingress line cards. In yet another implementation, atleast one of the ingress and/or egress line cards may include bufferingwhile at least one other one of the ingress and/or egress line cards maynot include such buffering.

It will also be apparent to one of ordinary skill in the art thataspects of the invention, as described above, may be implemented in manydifferent forms of software, firmware, and hardware in theimplementations illustrated in the figures. The actual software code orspecialized control hardware used to implement aspects consistent withthe principles of the invention is not limiting of the presentinvention. Thus, the operation and behavior of the aspects weredescribed without reference to the specific software code—it beingunderstood that one of ordinary skill in the art would be able to designsoftware and control hardware to implement the aspects based on thedescription herein.

No element, act, or instruction used in the present application shouldbe construed as critical or essential to the invention unless explicitlydescribed as such. Also, as used herein, the article “a” is intended toinclude one or more items. Where only one item is intended, the term“one” or similar language is used. Further, the phrase “based on” isintended to mean “based, at least in part, on” unless explicitly statedotherwise,

1. A method performed by a device, comprising: identifying, via acentral switching fabric of the device, a data unit; determining, viathe central switching fabric, that the data unit is a partial data unit,the partial data unit being a data unit that is less than fully filledwith data; increasing, via the central switching fabric, a partial countwhen the data unit is the partial data unit; determining, via thecentral switching fabric, that the increased partial count is greaterthan a threshold; and filling, via one or more of a plurality of ingressunits associated with the device, a subsequent data unit with data,where the subsequent data unit is filled to form a complete data unitwhen the partial count is greater than the threshold.
 2. The method ofclaim 1, where the plurality of ingress units connect to the centralswitching fabric; the method further comprising: receiving a stream ofdatagrams at one of the ingress units; forming, by the one of theingress units, the data unit from one or more of the datagrams;determining, by the one of the ingress units, whether to send the dataunit to the central switching fabric as a partial data unit or as acomplete data unit; and sending, by the one of the ingress units, thepartial data unit or the complete data unit to the central switchingfabric.
 3. The method of claim 2, where determining whether to send thedata unit includes: determining that another datagram has been receivedfor the data unit, and determining that the partial data unit is to besent to the central switching fabric when no other datagram has beenreceived for the data unit.
 4. The method of claim 2, where determiningwhether to send the data unit includes: waiting a predetermined amountof time, and determining that the partial data unit is to be sent to thecentral switching fabric when the complete data unit has not been formedwithin the predetermined amount of time.
 5. The method of claim 1, wherethe plurality of ingress units connect to the central switching fabric;and the method further comprising: forming the data unit at one of theingress units; and sending, by the one of the ingress units, the dataunit to the central switching fabric.
 6. The method of claim 5, furthercomprising: notifying, by the central switching fabric, the one of theingress units to send no additional partial frames when the partialcount is greater than the threshold.
 7. The method of claim 6, wherefilling a subsequent data unit with data to form a complete data unitincludes: holding, by the one of the ingress units, the subsequent dataunit until the subsequent data unit is completely filled with data. 8.The method of claim 5, where determining whether the data unit is thepartial data unit includes at least one of: checking a field in a headerof the data unit sent from the one of the ingress units to determinethat the data unit is the partial data unit, or checking a notificationmessage sent from the one of the ingress units to determine that thedata unit is the partial data unit.
 9. The method of claim 1, whereincreasing a partial count includes: maintaining a plurality of partialcounters, determining one of the partial counters associated with thedata unit, and increasing the partial count associated with thedetermined one of the partial counters by one when the data unit is thepartial data unit.
 10. The method of claim 1, where determining that thepartial count is greater than a threshold includes: maintaining aplurality of programmable thresholds, determining one of theprogrammable thresholds associated with the data unit, and comparing thepartial count to the determined one of the programmable thresholds. 11.The method of claim 1, where the data unit is a frame that stores one ormore datagrams or a superframe that stores a plurality of frames. 12.The method of claim 1, further comprising: storing the partial data unitand the complete data unit in a memory.
 13. The method of claim 1,further comprising: storing information associated with the partial dataunit and the complete data unit in a queue to await transmission.
 14. Asystem, comprising: means for determining that a data unit is a partialdata unit or a complete data unit, the partial data unit being a dataunit that is less than fully filled with data, the complete data unitbeing a data unit that is fully filled with data; means for increasing apartial count when the data unit is the partial data unit; means fordetermining that the partial count is greater than a programmablethreshold; and means for holding a subsequent data unit until thesubsequent data unit is formed into a subsequent complete data unit whenthe partial count is greater than the programmable threshold.
 15. Thesystem of claim 14, further comprising: means for forming the data unit,and where the means for determining that the data unit is the partialdata unit further includes: means for checking a field in a header ofthe data unit to determine that the data unit is the partial data unit,or means for checking a notification message sent from the means forforming the data unit to determine that the data unit is the partialdata unit.
 16. The system of claim 14, where the means for increasingthe partial count includes: means for maintaining a plurality of partialcounters, means for determining one of the partial counters associatedwith the data unit, and means for increasing the partial countassociated with the determined one of the partial counters by one whenthe data unit is the partial data unit.
 17. The system of 14, where themeans for determining that the partial count is greater than theprogrammable threshold includes: means for maintaining a plurality ofprogrammable thresholds, means for determining one of the programmablethresholds that is associated with the data unit, and means forcomparing the partial count to the determined one of the programmablethresholds.
 18. A device, comprising: a set of ingress units, one of theingress units to: receive a plurality of datagrams, form a frame fromone or more of the datagrams, and output the frame, and a centralswitching fabric connected to the ingress units, the central switchingfabric to: determine whether the frame from the one of the ingress unitsis a partial frame, the partial frame being a frame that is less thanfully filled with data, determine that a number of partial frames isgreater than a threshold when the frame is the partial frame, and notifythe one of the ingress units to send complete frames when the number ofpartial frames is greater than the threshold, where the complete framesare frames that are completely filled with data.
 19. The device of claim18, where when determining whether a number of partial frames is greaterthan a threshold, the central switching fabric is to: maintain aplurality of partial counters, maintain a plurality of programmablethresholds, identify one of the partial counters and one of theprogrammable thresholds associated with the partial frame, and compare acount value associated with the identified partial counter to athreshold value associated with the identified programmable threshold,and determine that the number of partial frames is greater than thethreshold when the count value is greater than the threshold value. 20.The device of claim 18, where said one of the ingress units is furtherto determine whether to send the frame as a partial frame or as acomplete frame.
 21. The device of claim 20, where said one of theingress units is further to determine that the partial frame is to besent to the central switching fabric when no other datagram has beenreceived for the frame.
 22. The device of claim 20, where said one ofthe ingress units is further to: wait a particular amount of time, anddetermine that the partial frame is to be sent to the central switchingfabric when the complete frame has not been formed within the particularamount of time.
 23. The device of claim 18, where notify the one of theingress units to send complete frames when the number of partial framesis greater than the threshold, the central switching fabric is to notifysaid one of the ingress units to send no additional partial frames whenthe partial count is greater than the threshold.
 24. The device of claim18, where the central switching fabric, when determining whether theframe is the partial frame, is further to at least one of: check a fieldin a header of the frame sent from the one of the ingress units, orcheck a notification message sent from the one of the ingress units. 25.A device, comprising: a set of ingress units, at least one of theingress units to: receive a plurality of datagrams, form a frame fromone or more of the datagrams, and output the frame; a set of egressunits; and a central switching fabric connected to the ingress units andthe egress units, the central switching fabric to: store a plurality ofthe frames as superframes in a memory, identify one of the superframesthat is ready to be sent to one of the egress units, determine that theidentified superframe is a partial superframe, the partial superframebeing a superframe that is less than fully filled with frames, determinethat a number of partial superframes is greater than a threshold, andcomplete said identified superframe when the number of partialsuperframes is greater than the threshold.
 26. The device of claim 25,where when determining whether a number of partial superframes isgreater than a threshold, the central switching fabric is to: maintain aplurality of partial counters, maintain a plurality of programmablethresholds, identify one of the partial counters and one of theprogrammable thresholds associated with the partial superframe, andcompare a count value associated with the identified partial counter toa threshold value associated with the identified programmable threshold,and determine that the number of partial superframes is greater than thethreshold when the count value is greater than the threshold value. 27.The device of claim 26, where said central switching fabric is furtherto maintain a plurality of queues, one of said plurality of queues isassociated with said one of the egress units, said identified partialcounter and said identified programmable threshold are associated withsaid one of said plurality of queues, and said one of the egress unitsis to acquire the identified superframe using information in said one ofsaid plurality of queues.
 28. The device of claim 25, where the centralswitching fabric is further to maintain a queue associated with said oneof the egress units, and where said one of the egress units is toacquire the identified superframe using information in said queue. 29.The device of claim 28, where the central switching fabric is further todelay providing said information in said queue to said one of the egressunits when completing the identified superframe.